Process of separating and recovering aliphatic acids



y 1939. cs. F. NADEAU El AL 2,165,293

PROCESS OF SEPARATING AND RECOVERING ALIPHATIC ACIDS Filed Feb. 12, 1936 50%): WATER 20110%ACETIC ACID s-wxaumac A010 5152Acnc 4cm 5-I5ZBlITYRIC 4cm oulvrmcummr EXTRACTOR smncmcncm wzrownvs DISTILLAT/ON COLUMN 95-1oo% BUTYRIO ACID INVENTORS:

Patented July 11, 1939 PROCESS 1 ING ALIPHATIC' ACIDS Gale F. Nadeau and ter, N. Y., assignors,

Abilities This, invention relates toprocesseskof separat-v ing and-recovering aliphatic acids andmorepare ticularly tona process of separating and recove eringyacetic ,andbutyrio acidtmixtures such as for example, obtained in a cyclic process for pro: duoing;cellulose-acetatebutyrate. ,-I a

i The separation, recoveryl'and tilization ofthe mixtures of aliphatic acidsobtained incvarious processes is a problem of-tgreat1technical,impor: tance. For example, certain processes such as the, manufacture of? cellulose acetate, butyrate byvprecipitation from 'its' reaction mixture: yields large quantities of-qacetic-butyric acid Imixtures and. it iswith these mixtures ,thatv our invention is particularly concerned. However; there, are

various other. sources of acetic-butyric acid mix: tures, suchasfor example, the-acid liquids to: getherawith lthelivari'ous impurities obtained by the .-,distillation of wood" may: comprise acetic: butyric acid mixtures. Also :mixed ."acids may-be produced by the .actionwof micro; organisms; Acids from .these' various sources are generally obtained in an aqueous'sta'teand must be separated andtcon'centratedin 'order: to obtain luse-x ful commercialproductsr Since butyric' acid and watenwill "form ;a mixe ture havingra constant boiling .pointnand; since acetic acid does not readily separate from v'vater, it is; apparent that aqueous acetic-'butyric. acid mixtures cannot be satisfactorily separated a'n-d recovered -by distillation alorie; 1 In fact; mere distillation alone-of an aqueous solution of acetic and butyric acids may @yield adistillateof acompositio'nlnot'much different from; the solution beingdistilled: I tis, therefore, obvious that to provide a simple 'processfior the separation and recovery of acid mixtures-which is efiici'enty-is a highly-desirable"result; i I Various processes for the separationand: re-

' covery "of aliphaticacidshave'*been' devised;

among which may 'be' 'mention'ed a method which consists m; first; dehydrating 1 the acids: either through neutralization and treatment with stil furic acid orby an azc0trop'ic distillation of the wat'en'from'the" aciduriixt'ur'e. Afterthe acids are dehydrated theyarefseparated by fractional distillation. ""It" has-and been proposed'to treat aqueous solutions 'ofacetic' and butyricacids with a 'x'sfater solubl-nor'nlal inorganicvsan or anaeid at 'least as strong as acetic and there'after-ex tracting the salted solution with-benzoLketohes orphenols. w w I p -Malm and Nadeauhave devisedcan extraction method :ior :separatingl acetic-butyric -mixture's,; and in particular, mixtures :v'from cellulose ace:

Eastman "Kodak Company,

- corporation of New Jersey I l r Webster"E-. Fisher," Boches= i by mesneassigninents, to

Rochesterg N'. Y- a tate butyrate manufacture by the use selective solvents 'such asdec'alin (decahydrdnaphthalene); It is with this, method that our process is primarily concerned, our process being animprovernent thereover.

vvWehave develope d'ja groupijofvselectivelexe ime a ents fl t seemin and er dilute alip latic acid mixtures which have proved to: be superior many respects to any. ereto,-

p fk owe ,tQ e rW -ih a w. y li l r' i for utilizing these ag ents, inasrnuch as 'these cient and f orm extracts from a t are; r

which t e x acidfcornp onent rnayfbe rea'dily ji e- WQr; 4-0 h 1 w I 1 ,This invention has as anfobject to provide a process for separating and recovering acetic and butyri wa .A further object'is 'to provide "a process which is applicable not only to relatively r rejw ier sq ai i s hec i i b d but also to the treatment ofrr'iixed acidsirom crude aqueous solutions such as obtained in the di$t lati9a t t d i li Object i to provides, process for the separation and recov er; oi butyric acidjxnixedfwith varying propor tions of other aliphatic acids, 'Another'object is-to providea process in whi the extract carrles with it, in addition to butyric acid, only a v r smal a o ta ii a i W erfurther object is to provide a process of a d separation in which, extraction isthe main fact I is al o anso i pr vi es o e s which wilLbe simple ,and inexpensive and yet applicableto-solutions containing any amounts of: acetic and butyric acids. Another object: is to provide an extracting gagent thatrernoves large amounts bf: butyric acid perunitof: extracting agents-z: A 1 still further object :is to 'provide a sol vent which produces an extract fromcwhich the acid component ma yzbe-readily recovered,

"Still another olojectis to provide a cyclic proce ess of-producingcellulose acetate butyrate ll'l-ivolvingithe step-of separating and recovering aliphatic acidsby extraction. 1 It is alsoanother object -to,-provide acontinuousprocess ofproducing celluloseacetate butyrate in which a va rietyoiselectivextracting agents may be employed for :recoveringacetic and 'butyric acids Other objects will:appearhereinafter. 1

- ta ned; in: sepa at'ngand. recovering ac ic a of certain butyric acids by selecting an extraction medium which will extract one of the acids from an aqueous solution without extracting the other acid.

Since acetic and butyric acids are homologues, considerable difliculty is encountered in selecting a liquid which is substantially immiscible with water; substantially immiscible with an aqueous solution of a mixture of acetic and butyric acids in varying amounts; and will remove substantially only butyric acid, accompanied by only small quantities of acetic acid, from such a solution.

We have found a group of solvent materials possessing these properties and the property of producing an extract from which the acid com.- ponent may be readily recovered. We have found that a number of chemical materials such as the halogenated hydrocarbons or hydrocarbons such as toluene could be used in separating butyric acid from acetic acid. The extracted butyric acid contains only small quantities of acetic acid, which can be removed in the final rectification of the recovered acid. In all instances the extract obtained was of such a character that the butyric acid could be readily recovered therefrom, as by distillation. In the instance of the toluene group of agents, these materials possessed the added and marked characteristic of permitting a separation of any small amounts of acetic acid in the extract as will be more fully described hereinafter.

Our preferred extracting agent, toluene, is therefore further distinguished by the fact that the extraction of butyric acid from aqueous solutions may take place over a wide range of mixed acid concentration, without the extract containing amounts of acetic acid which interfere. Furthermore, the extract does not require extensive treatment in order to recover the butyric acid.

Our process may be carried out in any apparatus of a known type although in commercial operations it is to be noted that we prefer to employ a system which includes counter-current extraction apparatus. For example, in carrying out our extraction on a production scale, the counter-current system would be employed in our cyclic process as follows: It is understood that the values set forth are merely for the purpose of illustration. Cellulose may be pretreated with a mixture of butyric and acetic acids and then esterification is carried out after the addition of acetic anhydride. The dope is then obtained by precipitation, for example, by using an acid precipitating solution. The precipitation liquid resulting is then separated by decantation or in some other suitable manner and countercurrently treated in a battery of counter-current extractors with a halogenated or toluene type hydrocarbon fully described herein. This selective solvent separates and permits the recovery of substantially all of the butyric acid. The acetic acid in the water layer from the countercurrent extractors then may be neutralized and the acid converted into acetic anhydride or the acetic acid may be concentrated by distillation in accordance with the procedure set forth in applications 513,989, 744,250 or 26,226 now Patent Nos. 2,028,800, 2,049,440 and 2,049,441, and then converted to the anhydride which is employed for the aforementioned anhydride additions in the esterification step.

We have found that our preferred agent comprising toluene possesses all of the desirable qualities of an organic solvent for use in the separation of mixtures of butyric and acetic acids by selective extraction. It is suitable not only when used in the separation of dilute mixtures but also in the separation of concentrated acid mixtures containing 50% or higher of mixed acids. This selective solvent, toluene, also known as phenylmethane is a hydrocarbon with the following formula:

ICHa

This selective solvent as well as the other solvents embraced by our invention are preferably employed in relatively pure condition but beneficial results may be obtained employing the solvents in admixture with other materials which do not detrimentally affect their function or one solvent may be mixed with another solvent. Hence, our invention in its broader aspects embraces any such diluted solvents and the use of our novel solvents either in the chemically pure or commercially obtainable form.

Further details concerning the use of our new selective solvents may be observed from a consideration of the following examples, the first concerning the halogenated group: 7

In a three-stage extractor about lbs. of a mixture containing approximately 9.7% butyric acid, 30.3% acetic acid, and 60.0% Water was extracted in a counter-current manner with about 117 lbs. propylene chloride. The water emerged from the extractor containing only about .4% butyric and 26.2% acetic acid. The propylene chloride emerged containing 7.2% butyric acid and 6.4% acetic acid. Thus the acid enters, containing 75.7% acetic acid of the total acid present and leaves containing at least 98.5% acetic acid of the total acid, while the emergent propylene chloride contains 53% butyric acid based on total acid. The propylene chloride was fractionated from the acetic and butyric acid mixture and this mixture, containing 53% butyric acid and 47% acetic acid is distilled if necessary and reused; for example, in the manufacture of cellulose acetate butyrate. The Water which now contains 26.2% acetic acid and 0.4% butyric acid may be concentrated by extraction with propyl acetate or by azeotropic distillation with ethylene chloride, propylene chloride or propyl acetate or in accordance with the procedure set forth in the aforementioned patents, or it may be neutralized, the water distilled oif and the acid converted into acetic anhydride. It may be desirable, before subjecting the extracted acid to some of these further separations to remove the small traces of propylene chloride which are dissolved in the extracted acid, by subjecting it to distillation to flash off the propylene chloride.

The above example is not necessarily the most efiicient way of carrying out the process. It may be desirable to vary the number of stages in the extractor or vary the ratio of propylene chloride to aqueous acid, depending on an economic balance between the degree of separation desired and the cost of achieving it.

While it may be seen from the above data that we have used propylene chloride and generally prefer this agent when employing a halogenated hydrocarbon, we do not wish to be limited to the exact agent shown since it has been given by way of illustration only, and there are other agents of their group which give useful hydrocarbons: it bein g understoodthat such other agents possess the,properties outlined with respe t to. et ne end-pr e lor d Nam ly, these agents must be capable of preferentially extrac in e tyfl acid, imm scibi i y w watenand incapableof iorminga constant boil;

ing mixture with butyric acid, Carbontetrachlorideand, flc wmethflene --h ve t eprope e W611. s, heop r v-t be-de e ib b ow w srz to t l e e namel l apab :of

forming an, azeot rop e with acetic acid.

These halogenated h dlQCa rbo a e a so, a;

, pable to'f extracting butyriefrom its aqueous th t n tn solutions when .not n, a mix ur w h o h r. aci sn a rrie. i a b r c e ed fr m-its aqueous d p abr, e ra ion ioll w d. .bY. d stillation of the extract. a i Considering now the group cf ,selectivesol en ne to th a om ti .w .Lsicle h ort u ne smi e ne ar cter ics these y o ar ons t b er le l iqte ere that eriorm c nsta t. bo lin mixtures ith acetic acid but not with; butyric acid. ,TIfhey will extract p butyric acid groin. an, aqueous solu tion in preference to acetic ,acid, and the 'a zeoe t o rabl c' 'r ain' en ugh. we a s6 Y e qla dfikm P-W he ex a t: inlea nt t r v wlien he a e; i f LL 'I' H 1 .Qne. wmaevndiwhh e9 he e e ndi iens is ewe. wh i rm ,zeotrop w th. i y ic acid, b .fdrm la I la fib i pawith. a et a d b i s at. 1.95" C dsenta n ng %a i a id by. -v is other v h d carb n and @1 9,- nat d hy o ar o sbpil n ab w n, t e en l limits ora out 10-.120f C.- w, c iu fit e ir ments are embraced by thisdnvention,

'The operation of-- ouraprocess.with the member toluene. is better; understood. by reference to. the accompanying. drawing; forminga; K part; :of; the present applicationl l .L. 1 Fig. 1 is a diagrammatic side elevation showing, in flow sheetarrangement, apparatus for carrying out our invention;=-:=In'= 1,.2 represents a continuous counter. current extractingsystem, either as :a unit or in a numbereof separate units.--Nu.- meral 3 represents :,:a 1 distillation column: At 4 there is fed into the'extracto'r anaqu'eous solution acid. 'At- Ethere' is fed into the vextra'ctor an equal weight of toluene containing about" '10 *acetic acid; this' mixture having been recoveredironi a point later in'the process; As thewe ali acid are: ceeds down diatom meter-vac acid is extracted'into theitoluene, alongfwith some-acetic acid; Althoughthe ext ractiyelpower of toluene and otherhydrocarbons for acetic .jacidisfvery 120 1 he. p e ev ,o iir ci ie, ai Qiintsfl 6f butyric acid increasesthe solubi litybfacetic acid. Ba e m tb waklaid hasrea h d s ne o n near: the middlepf. the extraction; systern suchas on T uli tant all al 9i ebu y ca h s been extracted by. the-toluenawhilethe acetic a d ha be nrfld i ed iromlwzz to bo -25%. The toluene leaving the ;t op-,- of, the extractor through pipe 8 at 9 contains both theaaceticiand butyric acid; and therefore contains about 9% acetic acid; and .9 i,1 i ac The; toluene. eXtract is then continuously conducted to the distillatiencolumnfi, which is so run that the acetic acidand tolueneare distilled from the top of the column,,.-While the butyricacid, sub stantially-freeof both, is removed from thebottom of, the column, eith er as vapororliquidc.

As already pointed'ouL-certainof .our new 5816C.- tive solvents, such as toluene, are characterized by being capable of forming an azeotrope with acetic acidin the, presence of butyricacid, and form no azeotrope,witnthe butyric.-. Consequently, the separation of any; aceticacidin the butyric is vcapsedto take place very-readily. A ,Thernixture of toluene and acetic vacidis then fed .irornthehead otthe distillation column, by conduit, Hi, preferably through a storage tank (not showm to, the lower endofthe extractor at 5, as outlined above. z 1 i W Now in; the absencecf-butyric acid, the distribution ratio of aceticacid between toluene and water is overwhelmingly in favor: of thewater. Hence, even though theweak acidgoingdown through the, extractor contains some 25% acetic, acid at zone 1- 1,it ,easilyextracts mostof the-acetic acid from thetoluene so thattby, the time the latter hasreached the zone ]'l. in the extractor, all but about 1% of the aceticacid has been extracted back into the aqueous layer. The toluene is then ready to proceed up thecolumn and: extract more butyric acid, while theweak acid emerging from the bottom of. the'extractor hasregained all of its original acetic ,acid; and mayberecovered by any of the many processes outlinedabove. It may be desirableto flash-.off, anytoluene .frornthe weak aceticacid, befOr'e the latter is recovered.

,I Ijhere, may be some variation in the apparatus could be .used, for both extractions, say being used.

for oneextraction one-day landv forthe other the next, though it is doubtfutiflthis would be as desirableas continuousoperation, 1 e

p -In the attachedidrawingwherein we have designated distillationlcolumns andthe like, these illus 4 trationsiare-nmerely. -diagrammatic. It will be 'andtechnique;used,;without departing from the understood thatthese figures embrace the use of.

condenserswapor feeds, reflux lines, storage tanks and similar, parts employed in distillation set-ups. ,While-we-have described ourwmethod of extraction as appliedto-theseparation of'acetic'and butyric acidmixtures because it is particularly adaptedthereto, ltheemethod has other applications.., M .p-Themethodusedfor this separation is new and novel in itself. This method may be'generically described as.::,.-(1).=,Theextractionof a solute A (butyric acid) @from asolventB (water) containinganother solute-C (acetic :acid) which; only by reason-:ofthe presenceof A (butyric' acid) is partially zextracted. vintofine -extracting solvent D (toluene) (2) .The separation of. the solute .A (but-yric acid).fr0m-the solventD (toluene) leaving solute-C; (acetic acid): in solvent D (toluene), by distillation-ion othermeans'; (3) The: re-extrac:-

return the solute C (acetic acid) from D (toluene) to B (water). It is only because of the presence of A (butyric acid) in D (toluene) that D (toluene) extracts some of C (acetic acid) and, now that A (butyric acid) has been removed, C (acetic acid) will again be extracted into B (Water).

Assuming toluene is to be employed in our new cyclic process of producing cellulose acetate butyrate, the following is a simple illustration of the steps:

An esterifying bath is prepared including butyric acid and acetic anhydride together with'acetic acid or a derivative thereof such as for example chloracetic acid. There may also be thoroughly incorporated into this bath a catalyst such as magnesium perchlorate, fused zinc chloride or other esterification catalyst. It is also possible to employ butyric anhydride and acetic acid rather than the combination stated.

As a source of cellulosic material to be esterified by this bath, we may employ cotton fiber tissue paper, clean cotton, surgical cotton wool, or carefully prepared bleached sulfite wood pulp. The cellulosic materials are thoroughly mixed into the esterifying bath which is maintained at a temperature sufficient to cause esterification. This will vary dependent upon the catalyst, reactants, etc. A clear mixture or dope results.

The cellulose acetate butyrate may be isolated by pouring the dope into water, separating, washing and drying the resulting ester. However, we wculd prefer to isolate the ester in a precipitation liquid having substantial acid content rather than by precipitation in water.

The mixed ester and the butyric-acetic acid containing liquid which surrounds it are separated by decanting, centrifuging or in some other suitable manner and the butyric-acetic acid solution is conducted to an extraction unit. This unit preferably comprises a plurality of counter current extractors wherein the butyric-acetic ture is brought in intimate contact with the selective solvent, preferably comprising toluene.

This solvent takes up substantially all of the butyric acid and only a small quantity of acetic acid. A water layer containing substantial amounts of acetic acid is obtained from the extractors and it can be converted into concenrated acetic acid and acetic anhydride to be used in the esterifying step. That is, the acetic acid remaining in the water layer may be neutralized, the water distilled 01f and the acetate resulting converted into acetic anhydride. 'Or the dilute acetic acid may be subjected to azeotropic distillation as already indicated by the procedure of application, 513,989, 744,250, or 26,226 now Patent Nos. 2,028,800, 2,049,440 and 2,049,441 to obtain concentrated acetic acid which can be pyrolyzed to yield acetic anhydride.

Thebutyric acid is easily recovered by a rectification of the extract as already described during which any moderate amounts of acetic acid present will be removed as a constant boiling mixture with the toluene. This is an important recovery feature.

The recovered acetic acid, together with any additional anhydride or acid to make up for materials lost or consumed in the reaction is employed in the esterifying step. Likewise the butyric acid is recovered, supplemented with more acid, and employed in the esterifying step.

There are a number of advantages derived from the cyclic process of producing cellulose acetate butyrate. The overall efliciency of the acid mix- 2,165,293 tion by B (water) of the solvent D (toluene) to cellulose acetate butyrate' process is greatly increased by being able to recover the acetic and butyric acids and put them immediately back into the process. The agents described permit a satisfactory separation and allow the recovery of the acids without the use of salts or other agents heretofore required in the prior art.

In the preceding description we have set forth numerous details concerning toluene, ethylene chloride and propylene chloride because these selective solvents are considered particularly satisfactory.

In our investigation we have also determined that there are other compounds which give useful results and which may be employed in the above described processes, such as for example: cyclohexane, cyclohexene, and methylcyclohexane, These agents are similar to toluene in that they form azeotropes'with acetic acid. For ex ample, cyclohexene formsan azeotrope containing about 6.5% acetic acid and methylcyclohexane forms an azeotrope containing about 31% acetic acid, therefore, We have shown a variety of agents which offer a considerable latitude of operation. These other agents are generically designated by the expression an inert organic liquid characterized by having a preferential solvent afiinity for butyric acid and substantial immiscibility with water, and incapable of forming a constant boiling mixture with butyric acid.

Having thus described our invention, what we declare asnew and desire to secure by Letters Patent of, the United States is:

1. In a process for the separation of acetic acid and butyric acid existing together in the form of an aqueous solution, the step which comprises extracting at least a part of said aqueous solution with a liquid essentially comprising a mixture of more than 5% acetic acid with at least one hydrocarbon from the group consisting of toluene, cyclohexane, cyclohexene and methylcyclohexane, ethylene chloride, carbon tetrachloride, trichlorethylene, propylene chloride, to obtain an extract containing at least a portion of said butyric acid.

2. The process of separating acetic and butyric acids existing together in the form of an aqueous solution, which comprises extracting the aqueous solution with a solvent essentially comprising toluene.

3. In a process for the separation of acetic acid and butyric acid existing together in the form of an aqueous solution, the step which comprises extracting at least a part of said aqueous solution with a liquid essentially comprising a mixture of more than 5% acetic acid with toluene.

4. The process of separating acetic and butyric acid existing together in the form of an aqueous solution which comprises extracting the aqueous solution with the solvent cyclohexene to obtain an extract containing cyclohexene, acetic acid, and butyric acid, and then subjecting the extract to a distillation treatment whereby an azeotrope of cyclohexene and approximately 6% acetic acid is evolved.

5. The process of separating acetic and butyric acid existing together in the form of an aqueous solution which comprises extracting the aqueous solution with the solvent methylcyclohexane to obtain an extract containing methylcyciohexane, acetic acid, and butyric acid, and then subjecting the extract to a distillation treatment whereby an azeotrope of methylcyclohexane and acetic acid is evolved.

' and then subjecting the extract to a distillation treatment wherein the solvent and acetic acid are removed and butyric acid obtained as a residue.

'7. In the cyclic process of producing cellulose acetate butyrate, including treating cellulosic material in a. bath which contains butyric and acetic compounds by steps which produce cellulose acetate butyrate, isolating the cellulose acetate butyrate in the bath in a manner which yields an aqueous solution containing acetic and butyric acids, the steps which comprise contacting at least a portion of this solution and a solvent from the group consisting of toluene, cyclohexane, cyclohexene and methylcyclohexane, ethylene chloride, carbon tetrachloride, trichlorethylene, propylene chloride, to obtain an extract liquid containing a substantial amount of butyric acid in the presence of solvent'and some acetic acid, subjecting the extract liquid to distillation for obtaining butyric acid therefrom.

GALE F. NADEAU.

WEBSTER E. FISHER. 

